The ethylene–receptor family from Arabidopsis : structure and function

Abstract

The gaseous hormone ethylene regulates many aspects of plant growth and development. Ethylene is perceived by a family of high–affinity receptors typified by the ETR1 protein from Arabidopsis . The ETR1 gene codes for a protein, which contains a hydrophobic N–terminal domain that binds ethylene and a C–terminal domain that is related in sequence to histidine kinase–response regulator two–component signal transducers found in bacteria. A structural model for the ethylene binding domain is presented in which a Cu(I) ion is coordinated within membrane–spanning α–helices of the hydrophobic domain. It is proposed that binding of ethylene to the transition metal would induce a conformational change in the sensor domain that would be propagated to the cytoplasmic transmitter domain of the protein. A total of four additional genes that are related in sequence to ETR1 have been identified in Arabidopsis . Specific missense mutations in any one of the five genes leads to ethylene insensitivity in planta . Models for signal transduction that can account for the genetic dominance of these mutations are discussed.